Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
International Journal of Current Microbiology and Applied Sciences
ISSN: 2319-7706 Volume 4 Number 12 (2015) pp. 831-843
http://www.ijcmas.com
Original Research Article
Assessment the Viability of Wastewater Treatment's Different
Technologies for Small Communities
Hanan A.Fouad*, Rehab M. El-Hefny and Fatma A. Hussein
Department of Civil Engineering, Faculty of Engineering – Shoubra, Benha University, Egypt
*Corresponding author
ABSTRACT
Keywords
Wastewater
treatment,
Technologies,
performance,
Effluent,
evaluation
The aim of this study is to evaluate the performance of wastewater treatment
technologies in four governorates in Egypt, which are Kafr El-Sheikh, Al-Gharbia,
El-Fayoum, and El-Sharqia. More than 25 full-scale wastewater treatment plants of
discharges ranged between 978 and 6000m3/day including oxidation ditches,
oxidation ponds, aerated lagoons, extended aeration, conventional aeration, rotating
biological contactors (RBC), upward-flow anaerobic sludge blanket reactor
(UASB), and compact units were assessed. The assessment has been carried out to
get the optimum wastewater treatment technology for small and rural communities;
and also for the improvement of wastewater quality to provide safe wastewater
reuse. The performance evaluation was done on the basis of removal efficiency of
biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total
suspended solids (TSS).Experimental results indicated that the wastewater
treatment compact unit achieved the highest removal efficiency in terms of BOD,
COD, and TSS which were 96.42%, 96.59%, and 95.47%, respectively. On the
other hand the oxidation ponds recorded the lowest removal efficiency of BOD,
COD, and TSS were 57.99%, 74.17%, and 50.13% respectively.
Introduction
Wastewater treatment in Egyptian villages
represents a dangerous challenge to
environment and public health. A limited
percentage of villages have recent facilities
for safe collection and wastewater treatment.
The number of rural wastewater treatment
plants in operation may not exceed 500,
while the total number of villages exceeds
5,500, so the number of desired sewer
systems in villages is far greater than the
number of established wastewater treatment
plants.
Wastewater is sewage originates from
household wastes, human and animal
wastes, Industrial wastewaters, storm runoff,
and groundwater infiltration (Metclaf,
2003).Wastewater treatment technologies
varied according to design organic loading.
Activated sludge technology has many
modifications (El-Sayed, 2010). Oxidation
ditch is a modified activated sludge
biological treatment process that utilizes
long solids retention times (SRTs) to remove
biodegradable organics (EPA, 2000).
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
It consists of an aeration single or multi
channel configuration within a ring, oval, or
horseshoe-shaped basin with one or more
rotating rotors for wastewater aeration
(Bitton, 2005). Extended aeration is used
primarily to treat wastewater flows from
small residential communities. Process
aeration is extended to 24 hours or more
(Mackenzieand Davis, 2010). It is just one
form of the conventional aeration system
(Ukpong, 2013). In this system screened raw
sewage are fed into the aeration tank without
primary clarifiers and maintained for a
period much longer than the case of the
conventional process. The rate of return
sludge is high. Oxidation ponds detention
time is usually 5 to 30 days. The ponds
receive no more pre-treatment than
screening. The system is a symbiotic
relationship between heterotrophic bacteria
and algae. Organic matter in wastewater is
decomposed
by
bacterial
activities,
including both aerobic and anaerobic. The
ponds can be classified in to: aerobic,
facultative, and anaerobic and maturation or
tertiary ponds (Hegazy, 2010; Okafor,
2011). Facultative ponds are Ponds 1 to 2.5
m deep, which have an anaerobic lower
zone, a facultative middle zone, and an
aerobic upper zone maintained by photo
synthesis and surface re-aeration. Anaerobic
ponds are Deep ponds that receive high
organic loadings used primarily as a
pretreatment process and are particularly
suited for the treatment of high-temperature,
high-strength wastewater.
consist of a series of closely spaced discs (3
to 3.5 m in diameter) mounted on a
horizontal shaft. The discs are rotated while
about one-half of their surface area is
immersed in wastewater (Sukumaran et al.,
2015).The discs are typically constructed of
lightweight plastic. It has been found that
the biomass composition of the discs within
the RBC plays a major role in the organic
biodegradation (Cortez et al., 2008). The
speed of rotation of the discs is adjustable.
When the process is placed in operation, the
microbes in the wastewater begin to adhere
to the rotating surfaces and grow there until
the entire surface area of the discs is covered
with a 1 to 3mm layer of biological slime
(Rongjun et al., 2015).
UASB operates as a suspended growth
system where micro-organisms attach
themselves to each other or to small
particles of suspended matter to form
agglomerates of highly settle able granules
that form an active sludge blanket at the
bottom of the reactor the gas formed causes
sufficient agitation. To keep the bed fully
mixed. In the UASB process, the waste to be
treated is introduced in the bottom of the
reactor (Ketan et al., 2014). The waste water
flows upward through a sludge blanket
composed of biologically formed granules
or particles.
The gas, produced under anaerobic
conditions, causes internal circulation which
helps in the formation and maintenance of
biological granules. The free gas and the
particles attached with the attached gas rise
to the top of the reactor (Pandya et al.,
2011). The success of the UASB reactor is
because of its high removal efficiency even
at light loading rates and low temperature,
low energy consumption, low sludge
production, low space requirements and low
nutrients compared to aerobic treatment
(Kathikeyan and Kandasamy, 2010).
Maturation or tertiary ponds are used for
polishing effluent from other biological
processes. It receives wastewater effluent
from secondary treatment systems Aerated
lagoons are Ponds oxygenated through the
action of surface or diffused air aeration.
They are widely used for small rural
communities up to populations of about
2,000 (Mackenzieand Davis, 2010). RBCs
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
September of the year 2013, the chemical
parameters BOD, COD, and TSS were
measured periodically.
Materials and Methods
Egypt’s governorates are enriched with
various wastewater treatment facilities
especially those of Kafr El-sheikh, ElGharbia, El-Fayoum, and El-Sharqia which
lie in the north and the middle Delta, Egypt.
More than 25 full-scale wastewater
treatment plants of discharges ranged
between 978 and 6000m3/day were assessed.
The investigated WWTTs were distributed
as follows: Four oxidation ponds (O.P.)
WWTPs lied in El-Fayoum governorate.
Two aerated lagoons (A.L.) WWTPs lied in
El-fayoum and Kafr El-Sheikh. Ten
oxidation ditches (O.D.) WWTPs lied in
Kafr El-Sheikh governorates. Five extended
aeration (Ext. Aer.) plants at El-Gharbia
governorate. Two conventional aeration
(Conv. Aer.) system WWTPs lied in ElFayoum and EL-Gharbia governorates. Two
RBC WWTPs at El-Gharbia governorate.
Two UASB WWTPs located at El-Gharbia
and El-Fayoum governorates, and one
wastewater treatment compact unit (C.U.) at
El-Sharqia governorate. This assessment of
WWTTs had been carried out to get the
optimum WWTT for small and rural
communities and also for the improvement
of the treated wastewater quality to provide
safe wastewater reuse. The collected data
include the description of each WWTP such
as actual and designed discharges, main
components
with
dimensions.
The
experimental study was conducted using
collected samples from the influent and
effluent flow of the WWTPs by the Holding
Company of Water and Wastewater under
the authority of the Holding Company of
Sanitary Drainage in Cairo, supervised
sampling, following and performing the
chemical analyses, Operation, maintenance,
and collecting the data in the laboratory of
each WWTP. Samples were collected from
the WWTPs in the months of summer and
winter (S&W) which were February and
Results and Discussion
The evaluation has been done through two
branches; the first branch was the laboratory
analyses that include the average summer
and winter BOD, COD, and TSS
concentrations and the average removal
efficiency have been deduced for eight
wastewater treatment technologies to be
assessed. The second branch is evaluation
the most economical alternative of the
different wastewater treatment technologies.
The value engineering was the used
approach. The value engineering can be
defined as the systematic application of
recognized techniques which identify the
function of a product or service, establish a
value for that function, and provide the
necessary function reliability at the least
overall cost (Cooper and Slagmulder, 1997).
Some chemical parameters were taken for
comparison because of their high selectivity
as point of efficiency of treatment.
Effect of Sewage Plant Variation on BOD5
Concentration
Figure (1) represents the concentrations of
BOD5 in the raw and treated wastewater for
the
eight
WWTTs.
The
average
concentrations of BOD5 of the raw
wastewater ranged from 275.125 to 629
mg/l. After treatment, wastewater treatment
compact unit secured an average of 22.5
mg/l O.D. Plants secured 23.31 mg/l, while
A. L. treatment plants secured 41.6 mg/l. the
4th group of RBC secured an average of
48.5 mg/l.
Figure (2) showed that the highest BOD
removal was obtained from the wastewater
treatment compact unit plants with about
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
96.42%.This
reflects
an
excellent
performance during all the treatment stages.
This might be attributed to the post tertiary
treatment using ultra filtration, moderate
organic loading, and sufficient follow-up.
While O.D. achieved high BOD removal
efficiency equal 95.02%.This performance
was higher than expected according to other
studied case histories that recorded 94.9 %
average removal efficiency of BOD5
(Hegazy, 2010). A. L. achieved a reasonable
BOD removal equal to 88.84% despite the
high organic loading in some plants like ElHasafa. RBC technology achieved a high
BOD removal equal to 88.84% when
compared with Rongjun et al., (2015) who
investigated that RBC achieves BOD
removal efficiency equal to 85%. Ext. Aer.
technology gives a moderate evidence for its
performance and secured BOD removal
efficiency equal to 86.71%, so the removal
efficiency of BOD was lower than expected
according to other case histories that
recorded (92-97.7%) average removal of
BOD, demonstrated in (Hegazy, 2010; AlSa’ed and Tomaleh, 2012). Conv. Aer.
System Showed unexpected performance of
BOD removal efficiency which was 80.40%,
this was lower than that reported in the
literature that showed BOD% ranged
between 85 and 97 %, as mentioned in
(Metcalf, 2003; Silvia et al., 2011). The
UASB system gives removal efficiency of
BOD equal to 62.62%. This result showed
that BOD removal efficiency of UASB
system was within the limits of BOD%
which ranges between 60 and 75 %, as it
was mentioned in (Metcalf, 2003; Silvia et
al., 2011). Finally O.P. achieved the worst
BOD removal efficiency which was57.99%.
8WWTTs. The average concentrations of
COD of the raw sewage ranged from 674 to
915 mg/l. Compact unit plants secured an
average of 29 mg/l in the treated sewage.
O.D plants secured 42.42 mg/l, while A. L.
and RBC treatment plants secured 73 mg/l.
the 8th group of O.P secured an average of
145 mg/l.
Figure (4) showed that the best COD
removal efficiency was obtained from the
compact unit plants with about 96.59%.This
reflects an excellent performance during all
the treatment stages. While O.D. achieved
high COD removal efficiency equal to
93.98%.This performance was higher than
expected according to other studied case
histories that recorded 85.60 % average
removal efficiency of COD (Metcalf, 2003).
A. L. achieved a reasonable COD removal
equal to 92.04% despite the high organic
loading in some plants like El-Hasafa. RBC
achieved a high COD removal equal to
89.23% when compared with (Rongjun et
al., 2015) who investigated that RBC
achieves COD removal efficiency ranged
between 60 and 80%%. Ext. Aer.
Technology gives a good performance and
secured COD removal efficiency equal to
87.91%, so the removal efficiency of COD
was within the limits according to other case
histories that ranged between 85.5 and
91%average removal of COD, demonstrated
in (Hegazy, 2010; Al-Sa’ed and Tomaleh,
2012). Conv. Aer. System showed a low
COD removal efficiency equal to 83.19%,
unlike it was higher than the BOD removal
efficiency, this value of COD removal was
lower than that reported in the literature that
showed COD % ranged between 87 and 93
%, as mentioned in (Metcalf, 2003; Silvia et
al., 2011). O.P. achieved COD removal
efficiency equal to74.17%, so the COD
removal efficiency was higher than that of
BOD removal efficiency. Finally, the UASB
system gives the lowest removal efficiency
Effect of Sewage Plant Variation on COD
Concentration
Figure (3) illustrates the concentrations of
COD in the raw and treated sewage in the
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
of COD that was equal to 72.41%.Although
this result showed that COD removal
efficiency of UASB system was within the
limits of COD % which ranges between 60
and 75 %, as it was mentioned in (Metcalf,
2003; Silvia et al., 2011).
system was within the limits of TSS% which
ranges between 65 and 80 %, as it was
mentioned in (Metcalf, 2003; Silvia et al.,
2011). Finally O.P. achieved the worst TSS
removal efficiency which was50.13%.
Effect of Sewage Plant Variation on Total
Average Removal Efficiencies of BOD,
COD, and TSS
Effect of Sewage Plant Variation on TSS
Concentration
Figure (5) showed the concentrations of
COD in the raw and treated sewage in the
8WWTTs. The average concentrations of
COD of the raw sewage ranged from 221.31
to 435 mg/l. After treatment, compact unit
plants secured an average of 21.5 mg/l. O.D
plants secured 26.64 mg/l, while A. L.
treatment plants secured 40.5 mg/l. RBC
secured an average of 46.75 mg/l.
Table (I) and figure (7) summarize, in a
similar way, the hall applied technologies.
The average influent, effluent concentrations
and the removal ratio percentage in terms of
BOD, COD, and TSS parameters have been
evaluated. It was recognized that compact
unit WWTP recorded the highest total
percent removal which was 96.16%. This
might be attributed to the post tertiary
treatment using ultra filtration, availability
of chemicals and spare parts to ensure ideal
operational
conditions
and
regular
maintenance period. On the other hand, the
oxidation ditches WWTPs have enjoyed
consistently good results insofar as
reliability and performance are concerned.
The total percent removal recorded
93.41%.This might be due to the long solids
retention times (SRTs) to remove
biodegradable
organics.
Meanwhile,
Oxidation ditches have typically complete
mix systems and constant water level. This
technology has a continuous discharge
which lowers the weir overflow rate and
eliminates the periodic effluent surge (EPA,
2000).
Aerated
lagoons
technology
significantly gives expected values for total
percent removal which were 90.50%. This
technology contains El-Hasafa WWTP
which has been excluded due to its high
organic loading, which significantly affected
its performance. This can be explained by
the high organic loading of the raw water
influent that contains animal’s wastes with
very large quantities. This high organic
loading produces high rates of Ammonia,
Figure (6) demonstrated that compact unit
plants recorded the highest TSS removal
about 95.47%.While O.D. achieved high
TSS
removal
efficiency equal
to
91.24%.This performance was higher than
expected according to other studied case
histories that recorded 85.6 %average
removal efficiency of TSS (Hegazy, 2010).
A. L. recorded a reasonable TSS removal
equal to 90.62%.While Ext. Aer. technology
secured TSS removal efficiency equal to
87.40%, so the removal efficiency of TSS
were lower than expected according to other
case histories that recorded94.8 %, as
mentioned in (Hegazy, 2010; Al-Sa’ed and
Tomaleh, 2012). RBC technology achieved
a good TSS removal equal to 87.21%.Conv.
Aer.
System Showed unexpected
performance of TSS removal efficiency
which was 72.95%, this was lower than that
reported in the literature that showed TSS%
ranged between 80 and 93 %, as mentioned
in (Metcalf, 2003; Silvia et al., 2011). The
UASB system gives removal efficiency of
TSS equal to 71.69%. This result showed
that TSS removal efficiency of UASB
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
heavy metals, H2S. As a result, the plant
consumes high quantities of Chlorine. This
leads to the presence of high levels of
Ammonia in effluent. On the other hand, the
surface aerators do not generate oxygen with
sufficient quantities to complete mixing in
the aeration tank and complete the biological
process (Fawzy, 2014). After that rotating
biological contactors system achieves
considerable total percent removal that is
equal to 88.41%. It was reported that RBC
performance may be due to Proper thickness
that should be about 2 mm. If too thick,
there may be loss of adhesion of the biofilms which may cause them to separate
from the bio-discs then loss of biomass in
basin, the sludge age was roughly 28–35
days so this resulting in slow treatment rate.
Other factors such as the spinning speed of
the bio-discs should be 1 rpm, and the biodiscs material should be noncorrosive
materials. Hydraulic retention time, high
temperature increase the bio-degradation by
the bacteria, no. of stages and hydraulic
loading also influence the treatment
effectiveness (Tawfik et al., 2006; Cortez et
al., 2008; Rongjun et al., 2015).
El-Gharbia governorate. Those plants have
not worked satisfactorily. This problem may
be attributed to problems in this plants’
operation. Where there was a malfunction or
damage in two from six mechanical surface
aerators of the aeration tank. This absolutely
leads to non contact and a less diffusion
between the air oxygen and the water
surfaces to give the chance to the bacteria to
degrade the organic constituents on the
aeration tank. On the other hand, there was a
low influent flow that was equal to
1280m3/day for Zawyat El- Karadsa and
2000m3/day for El-Moatamadia. This actual
flow was lower than the designed one. It
was equal to 3000m3/day Zawyat ElKaradsa
and
4000m3/day
for
ElMoatamadia.
These problems
make
achieving of high removal efficiencies more
difficult. This low performance can be due
to the Biological foams or scums, formed on
the liquid surface of activated sludge plants.
The stable foam is grey to cream-brown in
color, quite heavy in consistency and up to
30cm deep. The scum or foams appear on
the aeration tank and then eventually cover
most of the liquid surfaces including that of
the final effluent from the plant (Mackenzie
and Davis, 2010). Activated sludge is highly
recommended for treatment of big
discharges produced from large cities
(Fawzy, 2014). During this study, it was
observed that the system of UASB WWTT
gives total percent removal equal to 64.28%.
Meanwhile, Oxidation ponds recorded the
lowest total percent removal that is equal to
60.76%; so this was the worst technology
among the all applied systems for small
communities in Egypt. These results may be
attributed to the improper cleaning of the
pond’s surfaces and the over flow at some
plants like El-Lahon and Kotta. This over
flow means high organic loading more than
the designed one. This also means achieving
a low performance and so bad results.
The extended aeration system comes after
that in the arrangement gives a moderate
evidence for its performance and secured a
total percent removal equal to 87.84%. This
performance may be attributed to the low
mixed liquor suspended solids (MLSS)
which should be within the range of
31000mg/l. the solids retention time (SRT)
and the oxygen concentrations in the
aeration tank also may be the reason for the
low performance where SRT ranges from
24-30hrs.Conventional Aeration system
performance was unexpected. The total
percent removal recorded 78.85%.This type
of treatment achieved low performance
because it was represented with two
WWTPs named Zawyat El-Karadsa at ElFayoum governorate and El-Moatamadia at
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
Table.1 Mean BOD, COD, and TSS Removal Efficiencies, According to
the Treatment Technologies
Item
No
WWTT
C. U.
O. D.
A. L.
RBC
Ext. Aer.
Conv. Aer.
UASB
O. P.
1
2
3
4
5
6
7
8
BOD
removal
%
96.42
95.02
88.84
88.78
86.71
80.40
62.62
57.99
COD
removal
%
96.59
93.98
92.04
89.23
87.91
83.19
58.53
74.17
TSS
removal
%
95.47
91.24
90.62
87.21
87.40
72.95
71.69
50.13
Total average
Removal
efficiencies
96.16
93.41
90.50
88.41
87.34
78.85
64.28
60.76
order of
the
system
1
2
3
4
5
6
7
8
Table.2 Values of Points of Comparison
Point of
Comparison
Code
O. D.
Electricity
Consumption
(kW/h/m3 )
Required Area
(m2/m3)
Labor
Productivity
(m3/Worker)
A
0.412
B
6.839
C
210
O.
P.
0.155
A. L.
0.310
25.43
7
1566
28.22
5
342
Alternatives
Ext.
Conv.
Aer.
Aer.
0.440
0.314
RBC
0.078
5
A
B
A2
B
2.273
12.18
0.167
240
338
333.3
3
333.33
50
C
A
C2
Table.4 The Normalized Weight of each Point in Percentage
Electricity (A)
Area (B)
Productivity (C)
Total
Raw
Weight
3
0
2
5
837
0.08
4.55
C
Point of Comparison
C. U.
3.671
Table.3 The Weight of the Desired Criteria
A
UAS
B
0.5
Normalized
Weight
60.00 %
0.00 %
40.00 %
100 %
Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
Table.5 Ranks of Points of Comparison
Point of
Comparison
Code
Electricity
Consumption
(KW/h/M3)
Required Area
(M2/M3)
Labor
Productivity
(M3/Worker)
A
Oxidation Oxidation
Ditches
Ponds
1.91
5.06
Aerated
Lagoons
2.53
Alternatives
Extended
Conventional RB
Aeration
Aeration
C
1.78
2.50
10.0
0
UASB
1.57
Compac
t Unit
9.81
10.00
B
0.24
0.07
0.06
0.45
0.37
0.73
0.14
C
1.34
10.00
2.18
1.53
2.16
2.13
2.13
0.32
Table.6 Score of Alternatives
Points of
comp.
Weight
Oxidation
Ditches
Oxidation Ponds
Aerated Lagoons
Alternatives
Extended Aeration
Conventional
Aeration
RBC
UASB
Compact Unit
Rank
Score
Rank
Score
Rank
Score
Rank
Score
Rank
Score
Rank
Score
Rank
Score
Rank
Score
151.93
1.78
107.04
2.50
150
10.00
600
1.57
94.2
9.81
588.7
Elec.
60.00%
1.91
114.3
5.06
303.87
2.53
Area
0.00%
0.24
0
0.07
0
0.06
0
0.45
0
0.37
0
0.73
0
0.14
0
10.00
0
Labor
Prod.
Total
40.00%
1.34
53.64
10.0
400
2.18
87.356
1.53
61.30
2.16
86.33
2.13
85.14
2.13
85.14
0.32
12.77
100.00%
167.96
703.87
239.29
168.34
838
236.33
685.14
179.3
601.5
Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
Fig. 1 Effect of Sewage Plant Variation on BOD5 Concentration
Fig.2 BOD5 Removal Efficiency of Different Technologies
Fig.3 Effect of Sewage Plant Variation on COD Concentration
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
Fig.4 COD Removal Efficiency of Different Technologies
Fig. 5 Effect of Sewage Plant Variation on TSS Concentration
Fig.6 TSS Removal Efficiency of Different Technologies
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Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
Fig.7 Effect of Different WWTTs Variations on total BOD, COD, and
TSS Removal Efficiencies
element (C), which is the labor productivity
has a weight factor that is two times superior
to that of element (B) which is the area of
land. The total weight factor of each item
depends on the total number of times that it
was mentioned in the Table (IV). This
means that the raw weight of element (A) is
3, the raw weight of element (B) is 0, and
the raw weight of element (C) is 2. In Table
(IV), the normalized weight of each point in
percentage has been introduced. Sources:
(Cortez et al., 2008; Hegazy, 2010; Fawzy,
2014).
Economical Evaluation of Different Plant
Groups
The points of comparison are the average
electrical power consumed to treat 1 m3 of
wastewater in kW/hr, the average required
land space in m2 to treat 1 m3/d of
wastewater, and the labor daily productivity
of treated wastewater in m3/worker. The
values are shown in table (II). The
evaluation methods steps are the weight of
the desired criteria and the analysis of the
desired criteria. In the first step, the weight
of the desired criteria has been extracted
from Table (III), in which the mutual weight
factors of each point of comparison against
the others are presented. From Table (III), it
was concluded that the element (A) which is
the electricity consumption has a weight
factor that is two times superior to that of
element (B), which is the area of land. This
means that the running cost of the electricity
consumption is more important than initial
cost of the land, based on rough estimate of
the initial and running cost during the whole
design period of the project. Also, the
element (A) which is the electricity
consumption has a weight factor that is one
time superior to that of element (C) which is
the labor productivity. On the other hand,
In the second step, the average values of
each element are transformed to rank based
on the ratios between values presented in
Table (II). And these ranks are presented in
Table (V). The analysis completes by
calculating the total score of each
alternative, which equals the summation of
the normalized weight multiplied by the
rank of each element of comparison, as
presented in Table (VI). The alternative that
gets the highest score should be the best
alternative under the normal conditions.
From Table (VI), the oxidation ponds,
rotating biological contactors and compact
unit systems have the highest scores. Under
the normal conditions, the oxidation ponds
841
Int.J.Curr.Microbiol.App.Sci (2015) 4(12): 831-843
and rotating biological contactors systems
are the most appropriate alternative at the
least cost, while the oxidation ditch is the
most expensive appropriate system. It was
expected that variations in the treatment,
construction, and design in the sewage
plants may lead to a difference in quality of
treated wastewater. Also, irregular timing
and operation of pump stations that
introduce wastewater to the plants may
create over flow and create problems in the
treatment. Most of the results for the treated
sewage showed a high efficiency treatment
with high percentage of removal of organic
matter and suspended solids. The change in
type and design of plant have nearly no
effect on the final effluent. The efficiency
may increase by a good trained staff, good
management and availability of spare parts
to ensure a good operation and regular
maintenance period (Hegazy, 2010).
aeration technology was moderate and
secured a BOD equal to 86.71%, COD equal
to 87.91% and 87.40% for TSS removal
efficiency. This performance was lower than
expected. The performance presented by the
conventional aeration plants, considering
organic matter removal, was significantly un
expected among the evaluated systems, this
system recorded removal efficiencies for
BOD equal to 80.40%; COD equal to
83.19%, and 72.95% for TSS removal
efficiency. The UASB reactors showed low
BOD and COD removal efficiencies and a
poor performance regarding TSS. The
performance achieved by the UASB reactors
was equal to 72.41% for BOD average
removal efficiency; 72.33% for COD, and
47.78% for TSS average removal efficiency.
UASB process provides a suitable method to
treat wastewater with high concentration of
suspended solids. The oxidation ponds have
achieved the worst performance among all
the studied technologies with a removal
values equal to 59.99% for BOD; 74.17%
for COD, and 50.13% for TSS. But it is
more suitable and applicable for the villages
with slightly high temperatures.
In conclusion, the study indicates that all
major pollutants were reduced in the
wastewater after treatment to the BOD,
COD and TSS. Hence study concludes: The
performance of the wastewater treatment
compact unit WWTT was the best one for
the discharges below 500m3/d. the overall
removal efficiencies of BOD was 96.42%;
COD was 96.59% and TSS was 95.47%.
This technology is applied for the packaged
plants. The oxidation ditch technology has
been proved a great performance for
different contaminants. The average removal
efficiency of BOD was 95.02%; COD was
93.98, and TSS was 91.24 %. The
performance of the aerated lagoons was
reasonable.
The
average
removal
efficiencies were BOD was 88.84%; COD
was 92.04%, and TSS was 90.62%.The
rotating biological contactors showed a good
performance in terms of BOD, COD, and
TSS removal, with significant percentages
equal to 88.78%, 89.23%, and 87.21%,
respectively. The performance of extended
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